Kinetics of synergism and inhibition of exocrine secretion: 1. Gastric secretion: effect and interplay of intestinal hormonal inhibitors in vivo and in mammalian in vitro. 2. Intestinal, pancreatic and biliary secretion: Structure-activity relations and interplay of glucagon, secretion, VIP and analogues in vivo. 3. Pancreatic secretion (in situ perfused preparation): assessment of hormonal kinetics and interplay in an optimally secreting gland in vitro. 4. Colonic transport (open sacs and short-circuited chambered preparation): define the effects of VIP, GIP and synthetic fragments on transport mechanisms. Synergism and inhibition of gastric and intestinal motor activity: 1. Kinetic interplay of VIP, secretin, glucagon, motilin and analogues on cholecystic, gastric and intestinal muscle in vitro. 2. Differentiation of hormonal inhibitory and stimulatory effects in terms of acetylcholine release and tissue changes of cyclic AMP and GMP. Mechanisms of gastrointestinal and pancreatic hormone release in vitro: 1. Release of pancreatic insulin, glucagon and gastrin: effects of VIP and analogues; interplay of VIP and other hormonal peptides; interplay of hormonal peptides with adrenergic and cholinergic agents. 2. Release of antral and intestinal gastrin: studies as above. 3. Release of intestinal VIP and enteroglucaton: studies as above. Perfusion and perifusion techniques used in all three instances.